In many applications it is of interest to determine the direction of arrival of a signal, such as cellular phones and other radio communication system. The determination of a direction of arrival of a received signal from one communications unit can be used to maximize the sensitivity of an antenna array of a second communications system to that direction as well as the directionality of the signal power transmitted in a return transmission. Determining an angle of arrival can also be useful in identifying malicious signals, for example, spoofing or jamming signals intended to disrupt operation of a radio frequency communication system or navigation system. For emergency (e.g., 911) calls from a mobile telephone, direction of arrival can also be used to locate the caller when global positioning system (GPS) data is not available.